Most dried fruit industrial processes and wineries require water treatment facilities to treat effluents returned to the environment. Such facilities typically represent a significant investment by the business/community, and the performance of the facility (or failure thereof) can seriously impact the environment and ongoing operations, both financially and in terms of operational continuity.
Many dried fruit (e.g., raisins, prunes, dried apricots, etc.) industries use a sun-dried method and need to wash off a fine coating of dust blown onto them from sandy soil with water before packaging. When it washes away the dust on the dried fruit, some of the sugar in the dried fruit also dissolves into the water. The wash water typically contains 2-4% sugar, creating a high biological oxygen demand (BOD).
To make raisins, grapes are harvested when they reach a minimum sugar content of 19% or higher and carefully and naturally dried in the sun. Once the raisins have dried sufficiently, they are placed in large bins to store until processed. To remove rocks, dirt and sand, and organic matter, high pressure rinses with large amount of water, vacuums, wash tanks, riffles and re-rinse cycles are applied. During the washing process, a large volume of wastewater containing sugar is generated and needs to be treated before it is released to sewers.
Raisin companies in California generally produce 300 k-320 k tons of raisins every year and produce 360K-480K gal of 2-4% sugar-containing wastewater every day, year round. This is an equivalent of 40.9-54.5 tons of sugar per day and can support about 1-2 MGPY biodiesel production. Raisin wastewater contains sugar, mostly glucose, but does not generally contain much nitrogen.
In wineries, a large quantity of wastewater generation occurs during the crush process when grapes are actively being processed into juice for fermentation. This process requires large amounts of clean water for washing newly harvested grapes and results in a large wastewater output with high BOD. During the crush season, pH, BOD, total suspended solids (TSS), and nitrate levels are elevated. BOD discharge levels can approach 5,000 ppm, with values as high as 20,000 ppm in wastewater systems.
Wineries generate a strong organic wastewater that is dependent on production activities. Dissolved constituents in the wastewater include sugars, ethanol, organic acids, aldehydes, other microbial fermentation products, and soaps and detergents from clean-up operations.
Winery wastewater typically is low in pH because of organic acids produced in the fermentation process. Winery wastewater generally has sufficient phosphorus but is generally deficient in nitrogen and other trace minerals, which are necessary for efficient biological treatment.
Variability in wastewater composition depends mainly on the season and the particular operations being conducted at any given time. Certain winemaking operations—such as cleaning of the crusher, pomace conveyors, presses, and fermentation tanks—can also generate high strength wastewaters. Other process to produce wastewater includes washing of storage tanks, bottling and other equipment, and wine racking.
California produces an average of 90 percent of total U.S. wine production, and produced 631,575,325 gallon of wine in 2009. The average winery loses 7% of product post-press. For every 100 liters of juice or wine that drains from the press, only 93 liters ends up on the customer's table: the rest is lost down the drain. It can be calculated that over 44 million gallon per year of grape juice or wine is wasted as a wastewater, even though the amount of wastewater and glucose percentage varies between crushing and non-crushing seasons.
Traditional wastewater treatment systems for high BOD wastewater from the dried fruit industries and wineries are anaerobic or aerobic biological systems which let microbes consume sugar content in wastewater and lower BOD level. The most common type of biological system is an aerated lagoon or pond. Activated sludge, sequencing batch reactors (SBRs), and artificial wetlands are used by some wineries. The treated wastewater from these ponds needs to have a BOD of 40 ppm or less (depending on the location of the winery) before the winery can discharge the water to the vineyards for irrigation. The discharge level of 40 ppm as well as the restriction of standing water in an irrigation field is regionally dependent and is regulated by the Regional Water Quality Control Board (RWQCB) or the local County Department of Environmental Health. If the BOD is allowed to exceed the limits, the irrigation water can create an odor in the pond and irrigated fields, which is offensive to the wineries' customers and neighbors. If the discharge levels are significantly higher than 40 ppm BOD, the irrigation water can develop a slime layer just under the soils surface, which ‘plugs’ the field. This slime layer blocks the soil percolation of the water into the soil, creating standing water.
Heterotrophic fermentation of microalgae provides higher bioproductivity than photosynthetic and autotrophic growth such as open-pond system or photobioreactor system. This bioproductivity can be even higher with controlled illumination (See PCT/US2010/049347, herein incorporated by reference). In these heterotrophic conditions, organic carbon sources are needed to provide energy to microalgae. It is important to identify low cost and sustainable sugar sources for economic and sustainable production of microalgal products such as biofuels (biodiesel, renewable diesel, and biopetroleum), lipids, carotenoids, polysaccharides, biopolymers, and other chemicals.
Traditional high BOD water treatment utilizes microbes such as bacteria for biological treatment, but microalgae have not been tested and/or analyzed. The present invention demonstrates that the wastewater from dried fruit industries, e.g. raisins, fruit juice, and wineries can be used as sugar feedstock to produce valuable microalgal products.